Piezoresistive sensor structures are widely used in pressure or force measuring. Generally, the prior art is replete with a number of patents that describe various configurations and methods of fabricating piezoresistive pressure sensing devices.
Generally, a piezoresistive device includes a bridge pattern of resistors, which are mounted or otherwise diffused on one side of a relatively thin diaphragm member. The diaphragm, which may be fabricated from silicon, and deflects upon application of a pressure thereto, causes the piezoresistors to vary their magnitude according to the deflection of the diaphragm. Differential pressure measurements can be accomplished using a differential transducer that provides an output indicative of the difference between two pressures.
In aircraft engines, and other applications, it is often desirable to measure relatively small differential pressures, which occur across a wide range of line pressures. For example—measuring 5 pounds per square inch differential (psid) with reference to 0 pounds per square inch absolute (psia), and subsequently with reference to 150 psia, may be desired.
This may conventionally be accomplished by porting the pressures to be measured to opposite sides of a single pressure-sensing element. However, this approach is largely insensitive to line pressure variation. More particularly, this single element approach can prove unreliable as porting requires using tubing and small cavities which are directly in contact with the media to be measured. The media is often a dirty, moist air, or other fluid, with particulate contamination. Accordingly, these tubes and cavities are largely incompatible for long term, reliable use with such media. Additionally, moisture can collect and subsequently freeze in the tubing or cavities causing damage to the device. Therefore, it is desirable to eliminate the need for both internal tubes and small cavities.